1. Field of the Invention
The present invention relates generally to methods and apparatus for texturing planar surfaces, and more particularly to an improved method and apparatus for laser texturing a magnetic recording disk substrate.
2. Description of the Prior Art
Conventional magnetic recording disk drives utilize a rigid rotatable disk, such as that shown at 10 in FIG. 1, having concentric data tracks 12 for storing recorded information and use a transducing head (not shown) which "flies" over the surface of the disk to read and/or write data onto the several tracks. The head is carried by an air-bearing slider that rides above the disk when the disk is rotating at its operational speed. The slider is typically carried by a flexible suspension that is biased toward the disk surface by a small spring force.
Disk drives known as contact start/stop (CSS) drives permit contact between the slider and the disk surface during stop and start operations when there is insufficient rotational speed to maintain the air-bearing separation therebetween. The disk surface is typically made as smooth as possible to improve wear resistance and preserve uniform magnetic properties. However, after a slider has been in stationary contact with a smooth disk surface for a period of time, a problem known as "stiction", caused by a variety of factors including static friction and adhesion forces between the disk and slider, can result in damage to the head or the disk when disk rotation is initiated. Furthermore, the rather fragile suspension used to support the slider is also subject to damage as the head is held back by stiction and then released from engagement with the disk as disk rotation is initiated.
In order to minimize the stiction effects, CSS drives often use a dedicated textured "landing zone" 14 near the center opening 16 so that the slider may be parked when the drive is not operational. This landing zone is comprised of a specially textured region of the disk wherein no data is stored and is typically textured before deposition of the magnetic layer and subsequent layers that make up the finished disk. However, these following layers are normally quite thin and replicate the texture of the underlying substrate. The resulting textured surface tends to reduce the stiction forces that would otherwise be encountered when the slider is in engagement with the disk.
Texturing of the disk substrate is often accomplished by focusing a pulsed laser onto the surface of a spinning disk with sufficient intensity to locally melt small portions 18 of the substrate which, upon cooling and resolidifying, leave geometric variations in the surface topography of the substrate. The characteristics of the resulting geometric variations, or texture features, are a unction of laser pulse-width, spot size and shape, and spot energy, and are usually in the form of craters or bumps formed in the substrate.
Two types of laser texturing apparatus are generally used. In one type, the disk is placed upon a spindle and rotated as a pulsed laser beam is focused on the areas of the disk to be textured. The disk is then removed from the spindle, flipped over and returned to the spindle to texture the opposite side. In a second type of apparatus, separate laser systems are simultaneously focused onto the top and bottom surfaces of the disk as it is rotated on a spindle.
The problem with the first type of apparatus is that its throughput is low because it takes two texturing cycles to complete a single disk. The second type of apparatus overcomes the throughput problem, since only one texturing cycle is required per disk, but suffers the disadvantage that, because all disks are not of exactly the same thickness, accurate focus of at least one of the laser beams requires the use of a precision autofocusing system. Furthermore, to permit loading and off-loading of the disk to a spindle without interfering with the laser optics requires that complex positioning mechanisms must be provided in order to both clear the optics of the disk during transfer and to step the laser beams with precision during the texturing operation.